Mate guarding and male mate choice in the chameleon Kosciuscola tristis (: )

Peter C. Mahoney, Nikolai J. Tatarnic, James C. O’Hanlon & Kate D. L. Umbers

Journal of Ethology

ISSN 0289-0771

J Ethol DOI 10.1007/s10164-017-0509-9

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1 23 Author's personal copy

J Ethol DOI 10.1007/s10164-017-0509-9

ARTICLE

Mate guarding and male mate choice in the chameleon grasshopper Kosciuscola tristis (Orthoptera: Acrididae)

1 2,3 1 Peter C. Mahoney • Nikolai J. Tatarnic • James C. O’Hanlon • Kate D. L. Umbers4

Received: 4 October 2016 / Accepted: 6 February 2017 Ó Japan Ethological Society and Springer Japan 2017

Abstract In the wild, male chameleon Introduction (Kosciuscola tristis) are frequently observed mounted on the back of females even when not in copula, and will fight Mate guarding, where males establish a close association off other usurping males. If this behaviour is mate guarding with a female either before or after mating, is a common and and reflects investment in male mate choice, then we effective strategy to avoid sperm competition (Alcock 1994; expect males to preferably guard females based on reliable Simmons 2001). It can occur where paternity benefits out- cues of quality. Cues for female quality likely include weigh the costs involved including time (e.g. Jarrige et al. female size and egg development that together may indi- 2016), energy (e.g. Elias et al. 2014), lost mating opportu- cate fecundity. We investigated male mate choice in the nities with other females (Parker 1974) and challenges from field expressed as mate-guarding preference, by comparing other males (e.g. Umbers et al. 2012). Pre-copulatory mate size and egg development in guarded and unguarded guarding allows males to secure future mating opportunities females. We found no difference between guarded and yet presents a risk as it requires investment before copulation unguarded females in measures of fecundity or body size. has occurred. As such, it is expected to occur where paternity The majority of females sampled did not contain any viable is driven by first male sperm precedence (Parker 1974; eggs. This finding suggests that male K. tristis indiscrimi- Grafen and Ridley 2004) or where it can reduce the likeli- nately guard females in a scramble mating system. hood of female re-mating (e.g. Elias et al. 2014). By guarding mates post-copula, males reduce the likelihood of Keywords Sexual selection Á Mating behaviour Á Alpine female re-mating and potentially achieve paternity through biology Á Sperm competition last male sperm precedence (Parker 1974). Given that mate guarding can involve ‘opportunity costs’, males should be selective as to which females they choose to guard (Parker 1974; Bonduriansky 2001). Male mate choice manifests in many forms including selective courting, male–male competition (display or combat), variable allocation of sperm, and mate guarding & James C. O’Hanlon (Parker 1974; Amundsen and Forsgren 2001; Bonduriansky [email protected] 2001; Reinhold et al. 2002; Edward and Chapman 2011). It 1 Department of Biological Sciences, Macquarie University, is expected to occur in systems where costs of mate search North Ryde 2109, Australia or assessment are low, female variability is high, and male 2 Department of Terrestrial Zoology, Western Australian investment in reproduction is high (Bonduriansky 2001). Museum, Welshpool 6986, Australia Mate choice by males has been less represented than female 3 Centre for Evolutionary Biology, School of Biology, choice in the literature, but has attracted significant interest University of Western Australia, Crawley 6009, Australia in recent decades (e.g. Bonduriansky 2001; Gaskett et al. 4 School of Science and Health, Western Sydney University, 2004; Preston et al. 2005; Barry and Kokko 2010; Dough- Locked Bag 1797, Penrith, New South Wales 2751, Australia erty and Shuker 2014). While studies of male mate choice 123 Author's personal copy

J Ethol are becoming more common, such choice tests are typically winter snowfall (June), and eggs overwinter in the soil conducted in laboratory environments. Field studies also (Green and Osborne 1994; Umbers et al. 2013). Solo males, offer valuable insights and may yield different results from solo females, and pairs where males are guarding females laboratory studies (Dougherty and Shuker 2014); For are all regularly observed in the field. Females are almost example, laboratory experiments with house finches (Car- always guarded by a male when they oviposit (Umbers podacus mexicanus) found that males selected for females et al. 2012). Males remain mounted during female ovipo- with bright plumage, but subsequent field studies revealed a sition, and additional males surround the pair and attack the strong, and previously undetected, role of female age in mounted male, whilst nearby non-ovipositing females male mate choice (Hill 1993). appear to be ignored (N.J.T. personal observation). Here, we investigate mate guarding in the chameleon grasshopper (Kosciuscola tristis) (Orthoptera: Acrididae) Data collection in the field. Chameleon grasshoppers are endemic to alpine regions of south eastern Australia (Umbers 2011; Tatarnic Sexually mature female K. tristis (n = 129) were collected et al. 2013; Slatyer et al. 2014) and exhibit characteristics from Dead Horse Gap (36°31.0320 S, 148°15.8970 E) near common to other groups where male mate choice Thredbo, NSW (9 am–3 pm, 3 April and 11 May 2012). occurs. Males and females occur in high densities, so costs When collected, females were either mounted by a male of mate search should be low. Male investment in repro- (n = 65) or not (n = 64). Females were not collected if duction appears to be high, as males are often observed they were mating or ovipositing at the time of sampling. guarding females by mounting on their backs for extended All females were frozen within four hours of collection and periods of time without copulation (K.D.L.U. personal kept at -20 °C until dissection. Because many specimens observation). Furthermore, males guarding females are were missing one hind leg at the time of collection (com- challenged for their position by other males, resulting in monly observed in the field), all specimens with two legs ferocious and damaging contests (Umbers et al. 2012). were weighed (JS-VG20 digital scale, Jennings Scale Whether this apparent guarding behaviour represents Company, Phoenix, USA) with one randomly chosen hind pre-copulatory or post-copulatory guarding is unknown. leg removed. We measured size (pronotum length and The mating system of K. tristis has not received significant width) using digital callipers (Sontax Australia). To research attention, and whether males are selective in their investigate whether males may be responding to female choice of females, or whether sperm precedence patterns mass relative to her body size, we calculated an index of occur, is also unknown. To test whether males exhibit body mass as the residual values of the linear relationship preferences for females in the wild, we compared the traits between pronotum length and body weight (herein referred of females that were guarded by males with those of females to as body mass index). Females were dissected and classed that were not guarded. As guarding a female represents a as either gravid or non-gravid. The eggs were counted and significant investment by males, we hypothesised that there removed, and weighed for total egg mass. would be a difference between guarded females and We were unable to collect data on the males that were unguarded females and that this difference may ultimately guarding the females, as upon approaching mounted pairs, confer a fitness advantage to the males. If males are pref- males would frequently jump off the backs of females into erentially guarding more fecund females, then we predict nearby vegetation. We were then unable to identify these that guarded females would be larger (Bonduriansky 2001; males amongst others, as K. tristis are abundant and occur Edward and Chapman 2011) and have greater egg mass than in high densities, making tracking individual males by eye unguarded females. Alternatively, if males gain fertilisation impossible. success through first male precedence (Simmons et al. 1994), males may preferentially guard non-gravid or lighter Data analysis females, as this may indicate early stages of egg develop- ment and a lower chance that the female has already mated Data were initially explored using factorial binomial (Butlin et al. 1987; Bonduriansky 2001). models to test for differences between guarded and unguarded females. However, this resulted in significance levels that were difficult to interpret and likely to be type I Materials and methods errors. We manually inspected the data to remove variables with high levels of co-linearity, and attempted to use for- Study species ward and backward stepwise methods to build a model. This did not remove issues with apparent false positives, Adult K. tristis emerge in late January, and egg laying nor did it improve models based on Akaike information typically begins in late February. Adults die with the first criterion (AIC) values. These issues, and a relatively low 123 Author's personal copy

J Ethol sample size for multiple logistic regression methods, meant 0.8 that a factorial model approach was deemed inappropriate. a b 0.7 Rather, we employed a conservative approach and present here a series of separate univariate binomial analyses using significance threshold values corrected for multiple com- 0.5 0.6 Weight (g) parisons (P \ 0.008). We tested whether the weight, body 0.4 size (pronotum length and width), body mass index, Body mass index number of eggs, and total egg mass of females were pre- 0.2 0.3 dictors of whether females were guarded or unguarded. All -1.5 -0.5 0.5 1.0 1.5 Unguarded Guarded Unguarded Guarded statistical analyses were carried out using R version 3.3.0 (R Development Core Team 2011). c d To assess whether these female characteristics could potentially serve as cues of fecundity, we used zero-inflated Poisson regression analyses to assess whether fecundity (number of eggs) correlated with female weight, body mass index, pronotum length, and pronotum width. We used the 5.0 5.5 6.0 6.5 7.0 Pronotum width (mm)

2 Pronotum length (mm) pscl package (Zeileis et al. 2008) and calculated pseudo-R 4.5 456789 values as in McFadden (1973). 4.0

Unguarded Guarded Unguarded Guarded

Results e f

The majority of collected females were non-gravid (78 out of 129). Of the guarded females, 63% were non-gravid, and of the unguarded females, 56% were non-gravid. We found Total egg mass (g) no evidence for differences between guarded and unguar- Number of eggs ded females in terms of body weight, body mass index, 0 10203040 pronotum length, pronotum width, number of eggs, or total 0.00 0.10 0.20 0.30 egg mass (Table 1; Fig. 1). Unguarded Guarded Unguarded Guarded There was no evidence for a correlation between number Fig. 1 Comparison of female a weight, b body mass index, of eggs and body mass index, or body size measured by c pronotum length, d pronotum width, e egg number, and f total pronotum width, or pronotum length (Table 2; Fig. 2). egg mass, between guarded and unguarded females There was a positive correlation between number of eggs and total weight of females (Table 2; Fig. 2). Table 2 Zero-inflated Poisson regression models investigating the relationship between female fecundity (number of eggs) and female morphology

2 Discussion Variable Z4 YRP

Male chameleon grasshoppers invest in mate guarding and Pronotum length (mm) -1.008 -3.801 0.004 0.314 engage in costly fights to gain access to females, even in Pronotum width (mm) -0.387 -0.173 0.016 0.698 the presence of unguarded females. As such, we predicted Weight (g) -5.200 -12.09 0.230 <0.001 Body mass index -0.057 -0.946 0.002 0.344 Table 1 Univariate binomial regression models comparing guarded Bold type indicates significance at p \ 0.05 and unguarded female characteristics assuming a significance level of P = 0.008 that males would exhibit preferences for the females into

Predictor variable Z127 P which they invest time and energy. However, we found no evidence that males select females based on fecundity, as Weight (g) -1.040 0.299 the presence, number and mass of eggs in females did not Pronotum length (mm) 0.130 0.897 differ significantly between guarded and unguarded Pronotum width (mm) 2.188 0.029 females (Fig. 1). In fact, the majority of guarded females Body mass index 0.428 0.668 were non-gravid. This is not to suggest that males preferred Number of eggs 0.965 0.334 non-gravid females, but is more likely due to the fact that Total egg mass (g) -0.134 0.893 non-gravid females were more common overall.

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40 a guarding has been reported in a number of insect species (e.g. Estrada et al. 2010; Kureck et al. 2011) and is com- 30 monly associated with first male sperm precedence (Sim- mons 2001). Furthermore, mating is known to induce egg

10 20 development and oviposition in numerous orthopteran spe- Number of eggs

0 cies via the transfer of compounds from the male accessory

34567 gland (e.g. Pickford et al. 1969; Lange and Loughton 1985; Pronotum length (mm) Murtaugh and Denlinger 1985). Male K. tristis may then be able to secure paternity of future clutches by securing the b earliest copulation with post-ovipositional females, thereby

30 40 gaining first male sperm precedence and stimulating further egg development. The possibility of pre-copulatory guarding is further evidenced by observations of adult males mounted

Number of eggs on penultimate-instar females early in the mating season 01020 (K.D.L.U. personal observation). 34567 The lack of male preference for fecundity in K. tristis Pronotum width (mm) suggests that their mating system functions as a scramble c competition in which males indiscriminately mount

30 40 females. This finding is in apparent contrast to accounts of costly fights between males for access to particular females 20 over others (Umbers et al. 2012). A lack of female varia- 10 tion, and/or the inability of males to detect cues related to Number of eggs

0 fecundity, may prohibit males from being able to exercise 0.0 0.2 0.4 0.6 0.8 1.0 mate choice. Female weight correlated with female Weight (g) fecundity (Fig. 2), however males may be unable to detect or distinguish this cue. There still exists a possibility that d mate choice occurs after guarding, and that guarding 30 40 reflects a form of mate assessment, in which case we will

20 not necessarily observe preferences at this stage (Bon- duriansky 2001); rather, we expect males to exert choice Number of eggs

010 subsequently by only initiating copulation with high-qual- ity females. Further supplemental manipulative experi- -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Body mass index ments and paternity analysis will assist in understanding the mechanisms underpinning mate guarding and fertili- Fig. 2 Relationship between female fecundity and a pronotum sation success in K. tristis. length, b pronotum width, c weight and d body mass index Acknowledgements This project was facilitated by funding from the Additionally, we did not find any evidence for males pre- Australian Biological Resources Study and in-kind support from ferring to guard heavier or lighter females, which could Thredbo Sports, NSW. We thank P. Lagos and O. Kazakova for indicate selection for either fecundity or first male sperm specimen collection, M. Herberstein for guidance and feedback, and A. Allen for statistical advice. The authors declare no conflict of preference, respectively. interest. There were no differences in the overall size or relative mass (body mass index) of females that were guarded or Compliance with ethical standards unguarded. Pronotum size is fixed throughout the adult life The authors declare no conflicts of interest. All in this study stage, and whilst it may correlate with a female’s maxi- were collected under permit from the NSW National Parks and mum potential fecundity, it is unlikely to serve as a reliable Wildlife Service and were studied in adherence with Australian eth- indicator of fecundity at a single point in time. Whether ical research legislation. pronotum size influences the ability of males to stay attached when guarding requires further investigation. Male K. tristis were frequently found guarding non- References gravid females, and are known to fight over ovipositing Alcock J (1994) Postinsemination associations between males and females at a time when they are unable to affect the paternity females in : the mate-guarding hypothesis. Annu Rev of the clutch being laid (Umbers et al. 2012). Pre-copulatory Entomol 39:1–21

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